1. Field of the Invention
The present invention relates to transporting a media sheet, and, more particularly, to an apparatus for aligning the media sheet.
2. Description of the Related Art
Imaging apparatus, such as a printer, include a media path for moving a media sheet from an input area, through an imaging area, and ultimately to an output area that is usually on an exterior of the apparatus. The media path includes a plurality of nips formed between opposing rolls that not only drive a media sheet along the media path but may also facilitate the alignment of the media sheet prior to reaching the imaging area to ensure that the images are positioned correctly on the media sheet. A misaligned media sheet at the imaging area may result in a print defect commonly referred to as skew.
Various types of sheet registration systems have been used to align a media sheet in a media path of an imaging apparatus. One common sheet registration system is one in which the media is aligned to the media's side edge by forcing the media against a continuous solid edge that is aligned perpendicular to the imaging unit and is parallel to the media path. This is typically called a reference edge alignment system. Another method is to align the leading edge of the sheet by buckling the leading edge of the media sheet until it reaches proper alignment such that the leading edge is parallel to the imaging unit and is perpendicular to the media path. This is typically called a center-fed alignment system.
The most common method to achieve center-fed alignment is the use of a spring loaded alignment assembly, also known as a deskew shutter. The alignment assembly typically has a plurality of pairs of arms that stop one side of the media sheet just long enough for the other side to align before the full width of the media sheet forces the alignment assembly to retract or rotate out of the way. This stalling of the leading edge allows media to align with the alignment assembly prior to imaging. This type of alignment has been referred to as a bump-align method. In this method, the media sheet can only best be aligned to the alignment assembly's contacting surfaces, so keeping these contacting surfaces in line with each other as well as aligned to the imaging apparatus is most critical. Further, the number of contacting surfaces in an alignment assembly varies depending on the sizes of media supported by the printer. For best results, the media sheet's leading edge should only contact the appropriate pair of arms, and these two contact points should be as far from each other as allowed by the media sheet's width. If standard narrow media sheet sizes are supported, there is typically a need to have six or more contacting surfaces. From a manufacturing standpoint, it becomes most difficult to keep all contacting surfaces in line with each other using conventional manufacturing processes (e.g. molding, over molding, etc.) and tolerances. This can lead to situations where the two contact points may not be the outermost contacting surfaces, resulting to a less than ideal alignment.
What is needed in the art is an apparatus for aligning media sheet that guarantees that the media sheet is contacting the appropriate outermost pair of arms for aligning the media sheet based on the media sheet size.